A Study Of The Thoracic Clinical Anatomy And A New Technique Of Pedicle Screws Placement

Study Design: Retrospective-Prospective study.Objective: To locate the projections of the medial wall of the thoracic pedicle, dural sacand spinal cord on the lamina, then identify a “forbidden zone” of pedicle screwplacement. To quantify the position of thoracic pedicle screw entry points on the laminaat various segments of the thoracic vertebrae in normal subjects and patients withadolescent idiopathic scoliosis and propose a new technique to select entry points usinga new landmark.Background: Thoracic pedicle screws have been widely used in thoracic surgeries, andthe placement of pedicle screws has been studied extensively. However, no reports havedescribed how to determine safe placement locations using anatomical landmark onlamina, Furthermore, there are only qualitative studies on selecting the entry point, nostudy has quantified the position of entry points up to now.Methods:110CT and61MRI images were reviewed. The most concave point at thejunction of the transverse process and the upper edge of the lamina was used aslandmark. The projection point of the transverse medial pedicle wall and the landmarkon the lamina were measured using CT. The distances between the transverse medialpedicle wall and the dural sac and spinal cord were measured using MRI. Distancesbetween the projections of the dural sac and spinal cord on the lamina and landmarkwere studied. Comparisons were made between normal patients and patiens with AIS.3-dimensional computed tomography (CT) reconstruction techniques were used to studythe morphology of thoracic vertebrae in110adolescents. A quantitative area was used toselect the entry point. Thoracic pedicle screw entry point was determined using the new landmark as reference and thoracic pedicle screws were placed in21patients.Postoperative CT scan was performed to assess the safety and effectiveness of this entrypoint selection technique.Results: The projection of the medial pedicle wall on the lamina was coincident withthe the landmark.The projection of the dural sac on the lamina (relative forbidden zone)was an area1.43-1.98mm medial to the landmark respectively in the lamina. Theprojection of the spinal cord on the lamina (the forbidden zone) was an area4.64-6.35mm medial to the landmark in the lamina. No significant difference existedbetween concavity and convexity in the epidural space, while spinal cord shifted towardthe concavity of the scoliosis in the apical vertebral region of AIS patients. Wedetermined that the accuracy of pedicle screw placing after positioning entry point usingthe quantitative area was significantly superior to that after positioning entry point usingthe traditional method (P <0.05).Conclusion: The measurements may help surgeons determine the locations of thepedicle, dural sac and spinal cord accurately and identify the forbidden zone on thelamina during the pedicle screw placement to avoid neurological injuries. The newtechnique quantifies the position of each thoracic pedicle screw entry point, whichmakes it has relatively high accuracy of screw placement. Tt is convenient, easy tooperate. This positioning technique can provide safe and accurate clinical guidance forselecting thoracic pedicle screw entry point.